A new study compares months of data on the usage of urban bike sharing systems in Boston and Washington, D.C., and finds that money—not time—is the biggest determinant of how much usage the bikes get.

How do we know that money, not time, most motivates riders? Simple: Ride lengths show sharp drop-offs at the 30- and 60-minute pricing boundaries imposed by most urban systems.

Other interesting statistics that emerged from the study:

Average ride length for registered (i.e., habitual) users was a short 14 minutes, with a peak at just 6 minutes.

Other long-term data indicates that commuters keep an informal "energy budget" for all types of urban movement, and allocate their forms of transportation as much as they can according to the total budget for the day. The average length of bicycle trips under this plan is 42 minutes. This suggests that bike-share rides are a "last mile" solution that people combine with a train ride or a walk to reach their final destination.

Tourists or occasional users averaged a much longer 54 minutes, but this likely includes stops along the way.

The four most popular routes in Washington, D.C. and the five most popular routes in Boston had 2,000–3,000 trips each, but that's out of 1,859,773 and 552,073 total trips respectively. The top 300 routes in both cities each had 500 trips or more.

As bike-sharing spreads around the globe, the will no doubt continue. The authors suggest creating financial incentives to promote further use of the pollution-busting systems, perhaps by dropping the cost of riding during rush hour, or giving people a grace period to reach a bike station located at the top of a difficult hill.

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